**Solution : **
Go to C:\program files\mysql\bin\
Copy this file libmysql .dll to C:\windows\system32\
System:
Windows XP
Why it occurred:
You originally installed a previous version of MySQL probably 4.+++ and then tried to install a new version MYSQL version 5++
Symptoms:
When you run your apache server you see this error in the error.log file of your Apache server
PHP Warning: PHP Startup: Unable to load dynamic library 'C:/Program Files/PHP/ext\php_mysql.dll' - The specified module could not be found.\r\n in Unknown on line 0
... and it happened despite php_mysql.dll already being in place* *